Abstract

Disulfide-bond A Oxidoreductase-like protein (DsbA-L) possesses beneficial effects such as promoting adiponectin multimerization
and stability, increasing insulin sensitivity, and enhancing energy metabolism. The expression level of DsbA-L is negatively
correlated with obesity in mice and humans, but the underlying mechanisms remain unknown. To address this question, we generated
reporter gene constructs containing the promoter sequence of the mouse DsbA-L gene. Deletion analysis showed that the proximal
promoter of mouse DsbA-L is located between -186 to -34 bp relative to the transcription start site. In silico analysis identified a putative Sp1 transcription factor binding site in the first intron of DsbA-L gene. Electrophoretic
mobility shift assay and chromatin immunoprecipitation analysis indicated that Sp1 bound to this intron region in vitro and
in intact cells. Overexpression of Sp1 or suppressing Sp1 expression by siRNA reduced or increased DsbA-L promoter activity,
respectively. The binding activity of Sp1 was gradually decreased during 3T3-L1 cells differentiation, and was significantly
increased in adipose tissues of obese mice. Our results identify Sp1 as an inhibitor of DsbA-L gene transcription and the
Sp1-mediated inhibition of DsbA-L gene expression may provide a mechanism underlying obesity-induced adiponectin down-regulation
and insulin resistance.